258. Add Digits
- Total Accepted: 134747
- Total Submissions: 269960
- Difficulty: Easy
- Contributors: Admin
Given a non-negative integer num, repeatedly add all its digits until the result has only one digit.
For example:
Given num = 38, the process is like: 3 + 8 = 11, 1 + 1 = 2. Since 2 has only one digit, return it.
Follow up:
Could you do it without any loop/recursion in O(1) runtime?
Hint:
- A naive implementation of the above process is trivial. Could you come up with other methods?
- What are all the possible results?
- How do they occur, periodically or randomly?
- You may find this Wikipedia article useful.
Code
class Solution(object):
def addDigits(self, num):
"""
:type num: int
:rtype: int
"""
if num == 0:
return num
elif num % 9 != 0:
return num % 9
else:
return 9
Idea
The result is called Digital root. Digital root will be equal to num % 9 except when num equals to 0 or num is itself 9’s multiples.